Penguin's e-books have been put back on the virtual shelves of America's libraries, a week after they were yanked for unexplained "security" reasons.

Penguin pulled its titles from e-book libraries last week after a kerfuffle between the publishers, library e-book suppliers Overdrive and Kindle-makers Amazon. The precise cause of the problem, described as a security concern by Penguin, remains unclear, though it was presumed to have something to do with copyright.

Though the back-catalogue of Penguin titles will return to US e-book libraries from today, Penguin will continue to withhold e-books of its new titles from libraries until a deal is reached. Paper versions of the new books will be provided to libraries as normal, and new e-books will be available for purchase.

Penguin said it was not commenting beyond the press release, which states that it is in discussions with Amazon and Overdrive:

Amazon has undertaken to work with Penguin and Overdrive between now and the end of the year to address Penguin's concerns. Penguin will, as a result, restore the supply of these titles until the end of the year in order to return the availability of older titles to all its digital customers.

In the UK, where far few libraries offer e-books, Penguin is doing the same thing: delaying the availability of new digital files to libraries until a deal is reached with both e-book suppliers and Amazon. ®